Parallel ganged multiple potentiometer



NOV. 28, 1967 F M WOLFF PARALLELGANGED MULTIPLE POTENTIOMETER OriginalFiled Aug. 16, 1963 2 Sheets-Sheet 2 @w25 ,wb

INVENTOR @EMP/ck /7 WO1-FF United States Patent O 3,355,694 PARALLELGANGED MULTIPLE POTENTIOMETER Frederick M. Wolff, Montclair, NJ.,assignor to `Century Lighting, Inc., Clifton, NJ., a corporation of NewJersey Original application Aug. 16, 1963, Ser. No. 302,595, now

Patent No. 3,307,133, dated Feb. Z, 1967. Divided and this applicationSept. 8, 1966, Ser. No. 577,995

4 Claims. (Cl. SSS-202) ABSTRACT F THE DISCLOSURE A parallel gangedmultiple potentiometer comprising a casing including numerous parallellinear slots in a wall thereof, numerous xed contacts and electricalprinted circuit means carried by an opposite wall thereof, the printedcircuit means including input busses, numerous ablatable resistancebands, electrically connected in parallel between the busses so as toeach induce a like voltage gradient, conductive abrasion-resistance tapsegments disposed in rows parallel to said slot axes, each row beingassociated with a different resistance band and said tap segments beingelectrically joined to their ailiated resistance band at axially spaceddiscrete points, and collector strips, each parallel to the slot axesand each electrically connected to a different fixed contact, and bridgecontacts mounted for sliding movement in the slots, each bridge contacthaving a head sloped for convenient gripping, a constricted neck joinedto the head and slidable within the associated slot, and a hollow bodyjoined to the neck and located within the casing, said body housing anelectrically conductive button riding along and thereby electricallyconnecting a collector strip to a selected tap segment of an associatedrow, whereby to selectively pick oif a desired voltage from along anassociated single voltage gradient and to lead said voltage to theassociated fixed contact, said button being non-rotatably mounted on thehead for sliding movement toward and away from the wall of the casingcarrying the circuit means and being urged toward said wall by a spring.

This is a division of application Serial No. 302,595, filed August 16,1963, now Patent No. 3,307,133.

This invention relates to a parallel ganged multiple potentiometer.

It is an object of my invention to provide an improved parallel gangedmultiple potentiometer which is light weight, rugged and compact and hasits voltage pickolfs adapted for convenient connection into a controlcircuit.

It is a further object of my invention to provide a parallel gangedmultiple potentiometer of the charatcer described wherein thepotentiometer voltage pickoifs are automatically locked in positionafter they have been brought to any selected point and wherein thepickolfs may be readily unlocked by quick manual manipulation and movedto another point after which they are again automatically locked inposition, whereby to prevent accidental or unintended movement of thevoltage pickotfs.

It is yet another object of my invention to provide a parallel gangedmultiple potentiometer of the character described whose construction isparticularly adapted to incorporate a printed circuit, resulting in acompact unit and affording economy of manufacture and ease in assembly.

It is another important object of my invention to provide a parallelganged multiple potentiometer of the character described which has anelectrical circuit that uses parallel printed carbon resistance bands tofurnish voltage gradients and which is so constructed that no abra-3,355,694 Patented Nov. 28, 1967 ICC sive wear is applied to these bandsso as to promote constant resistance and long life for the unit.

These and various other objects and advantages of my invention willbecome apparent to the reader in the following description.

My invention accordingly consists in the features of construction,combinations of elements and arrangements of parts which will beexemplified in the device hereinafter described and of which the scopeof application will be indicated in the appended claims.

In the accompanying drawings in which is shown one of the variouspossible embodiments of my invention,

FIG. l is a fragmentary plan view of a parallel ganged multiplepotentiometer constructed in accordance with my invention;

FIG. 2 is a fragmentary top View of the upper face of the bottom wall ofmy potentiometer on which are im printed collector, tap and resistancecomponents;

FIG. 3 is an enlarged fragmentary view of an end portion of the wallshown in FIG. 2;

FIG. 4 is an enlarged fragmentary cross-sectional view takensubstantially along the line 4-4 of FIG. l;

FIG. 5 is an enlarged fragmentary cross-sectional side view takensubstantially along the line 5 5 of FIG. 4;

FIG. 6 is an enlarged fragmentary partially broken away perspective viewof a sliding bridge contact and the cooperating printed components ofthe potentiometer;

FIG. 7 is an enlarged exploded perspective view of the several parts ofthe sliding bridge contact;

FIG. 8 is a partial schematic diagram of the electric circuit providedby my potentiometer; and

FIG. 9 is a fragmentary cross-sectional view taken substantially alongthe line 9-9 of FIG. 7.

Referring now in detail to the drawings, the reference numeral 10denotes a parallel ganged multiple potentiometer constructed inaccordance with my invention. A hollow dat elongated casing 12 housesand supports the several other components of the potentiometer and iscomposed of light weight electrically non-conductive tough material. Thecasing 12 comprises a shell 14 and a flat bottom wall 16, both of theseparts being elongated and generally planar, and substantially of thesame plan contour and dimensions. The shell is preferably formed from ahigh impact thermo-plastic resin such as anacrylonitrile-butadiene-styrene polymer. A plastic material sold asCycolac by the Marbon Chemical Division of the Borg-Warner Corporationhas been found suitable. The bottom wall is preferably formed fromfabric plies impregnated with a phenol formaldehyde condensation resin.The shell 14 and the bottom wall 16 define therebetween an elongatedrectangular enclosed operating space 18 and to this end, short sidewalls 2t), unitary with the shell 14, depend downwardly therefrom so asto space the top wall of the shell from the wall 16, said side wallsbeing joined at their bottom edges to the top surface of the bottom wall16 as by screws 22. The screws 22 pass through countersunk apertures 24in the bottom wall 16 and are threaded into aligned tapped bores 26 inthe side walls 20.

The top wall of the shell 14 includes numerous elongated parallel spacedslots 28 of uniform width over their major portions which slots extendthrough the shell and are transversely disposed to the length of thecasing 12. Each slot is narrow as compared to its length and each liesalong parallel axes. Preferably, these axes are linear and are mutuallytransverse to the length of the casing 12. Every slot 28 is outlined byan adjacent narrow low ridge 30 on the top surface of the shell 14.There may be as many slots as desired for a particular installation,and, as will shortly be described, each slot is associated with adifferent single potentiometer voltage pickoif. I

utilize 30 slots (and therefore 30 potentiometer voltage pickois) in atypical embodiment of my invention.

A sliding bridge contact 32 rides in each of these slots 28 and ismounted for parallel movement, i.e. is adapted to be selectively moved,as by the `hand of a user, to any desired position along its affiliatedslot. Raised numerical indicia 34 and raised index lines 36 are disposedalongside each slot with which a raised index bar 38 yon the top of eachsliding bridge contact 32 may be aligned to indicate the relativeposition of the bridge contact 32j along its associated slot 28.

As each bridge contact 32 is similarly constructed, only y one will bedescribed in detail. The bridge contact 32 has an enlarged flat-bottomedhead 4? whose top surface is slopingly contoured for convenient pushingor gripping by a hand of a user. The width of the head 4t) is greaterthan the width of the slot 28 so that the bridge contact 32 cannot fallthrough the slot. The planar bottom surface of the head 40 slides alongits affiliated slot on the raised low ridges 30 adjacent each top sideedge of the slot.

A constricted neck 42 depends from the head 40 of the sliding bridgecontact 32 and unitarily joins the head to a cubical hollow dielectricbody 44 of the bridge contact. The neck y42 is slightly narrower thanthe width of the slot 28 to permit it to slide within the slot and yetis wide enough to prevent excessive movement therein. The neck iselongated in a direction parallel to the length of the slot and isformed with parallel side walls whereby to prevent twisting movement yofthe neck in the slot.

Longitudinal ribs 46 run along the underside of the top wall of theshell 14 and are unitary therewith. Each rib 46 runs midway between twoadjacent slots 28 from the front to the rear side walls 2li. The ribs 46serve to strengthen the shell 14 and to physically isolate the variousbridge contacts from one another in the event any particular bridgeContact should break and no longer be confined by its ailiated slot.

A section of the casing, eg. the under surface of the top wall of theshell 14 is serrated to form a multitude of mutually parallel tiny teeth48 which are elongated parallel to the length of the casing 12, i.e.transverse to the slots 2S, and are interrupted by the slots. Anabutting section of the bridge contact 32, e.g. the top surface of thesliding bridge contact body 44, also includes parallel teeth 50 ofmatching contour and dimensions for disengageable conection, i.e.engagement, with the teeth 48 on the shell undersurface.

Spring means 58 biases the bridge contact 32 upwardly so that the teeth50 on the upper surface of the bridge contact body 44 are urged intoengagement with the teeth 48 on the bottom surface of the shell 14 alongthe slots 28 whereby to lock the sliding bridge contact in any desiredposition along an associated slot. This engagement eliectively restrainsthe bridge contact from undesired or accidental movement along the slot28 that might be cause-d by vibration of the electrical unit in which mypotentiometer 10 is installed, or by an unintended light touch by thehands or body of a user.

The neck 42, when the teeth 48, t) are engaged, holds the under surfaceof the head 40 spaced from the low ridge 30 on which it rides. Downwardforce exerted by the hand of a user on the head 40 overcomes the springmeans biasing force and moves the body 44 downwardly to clear the bridgecontact teeth 50' from engagement with the shell teeth 48. This permitssliding movement of the bridge contact 32 along the slot 28 and hencemovement of the bridge contact body 44 within the operating space 18.

The bridge Contact body 44 houses within the downwardly opening hollowwell del-ined by its side walls a conductive portion, e.g. an upwardlyopening cup-shaped bridge button 52 formed from an electricallyconductive material, such as brass. Two diametrically opposed nibs 53,55 protrude downwardly from the bottom of the bridge button 52 and areintegral therewith. Said nibs are spaced apart in the direction of thelength of the casing 12. The button 52 projects downwardly from the body44 and is slidably mounted for vertical movement relative to the bridgecontact body 44. To this end, the interior of the body 44 deiines inpart a downwardly opening substantially cylindrical bore (well) ofslightly larger di ameter than the button 52. The button S2 slides inthis bore. The top edge of the button 52 has two diametrically opposedtabs 54 extending radially outwardly therefrom which slide with thebutton 52 and which ride in opposed vertical through slots 56 in theside walls of the body 44. The tabs 54 limit downward movement of thebutton 52 beyond a point at which the tabs 54 abut the closed bottomends of the slots 56. The tabs also restrict relative rotation betweenthe button 52 and the body 44, when the tabs are within these slots.

A helical coil spring 53 disposed within the top portion of thecylindrical bore within the body 44 urges the bridge button 52downwardly and into electrical contact with lines of the printed circuit66. The biasing action by the coil spring 58 on the button 52simultaneously causes an opposed upward force on the sliding -bridgecontact body 44 forcing the body teeth 50 into engagement with the teeth43 on the shell bottom surface, as previously described.

A laterally disposed open-ended through slot 60 in the top portion ofthe body 44 and internal inwardly and downwardly opening verticalopposed entry grooves 62 in the body 44 are provided for assembly of thesliding bridge contact 32. The slo-t 60 passes through the pair ofopposed body walls in which the slots 56 are contained and is connectedtherewith, the grooves 62 being formed within the other set of opposedbody walls. The distance between the grooves 62 and their width issufficient to allow entry of the button 52 and its tabs 54.

In assembly of the bridge contact 32, first the helical spring 58 isplaced in the cylindrical cavity within the body 44 and thereafter thebridge button 52, tab-endfirst, is slid upward as by the assemblerslinger against the force of this spring, the tabs 54 sliding in theinternal grooves 62. When the tabs S4 have been slid to the ends of thegrooves 62 and into the through slot 60, the button 54 is axiallyrotatel 90, the slot 60y preventing interference between the rotatingtabs 54 and the body walls. After the rotation, the tabs 54 will beabove and in alignment with the vertical slots 56, into which, uponrelease, they are directed by the biasing force of the coil spring 58.This completes the assembly of the sliding bridge contact 32 theconverse order of steps being taken for disassembly. The bridge contacts32, after they are assembled, enter the slots 28 from beneath by meansof enlarged openings 64 on the ends of the slots, these openings beingdimensioned to allow entry only of the head 40 and not the body 44. Thebottom wall 16, when subsequently joined to the shell 14, is spacedclosely enough to the shell so as to prevent the sliding bridge contacts32 from falling through openings 64, should any contact be slid to thisarea.

The bottom wall 16 of the casing 12 is flat, as has been mentioned, andcarries thereon a printed circuit 66, on iparts of which the bridgebutton nibs 53, 55 ride. The printed circuit is placed on the bottomwall 16 by standard processes, such as dipping, printing or plating,being formed with a copper base and a tin or rhodium cover layer orplate. A hard electrically conductive material such as rhodium ispreferred to reduce wear due to continual sliding movement of the bridgebutton 52 over components of the printed circuit. The printed circuit 66includes numerous parallel electrically conductive printed straightcollector strips 68, each of which runs parallel to and approximatelyunderneath an aiiiliated diferent slot 28 `in the shell 14. The strips68 are all of like uniform width and length. The collector strips 68 atone of their ends are each joined to a separate iXed contact 70, whichis adapted to be electrically connected into the electrical circuit withwhich the potentiometer will be used, as indicated by the arrows A inFIG. 2.

Each fixed contact 70 is mechanically joined to the bottom surface ofthe bottom wall 16 as by a rivet 72 which passes through the contact andthe bottom wall, and each contact has one L-shaped end 74 which passesthrough the bottom wall and is joined to the end of an atiliatedcollector strip 68 as by solder at 76. The front end 78 of each fixedcontact 70 is upwardly curved and lies in a matching groove in the frontside wall 20 (see FIG. 5). As the bridge contact 32 slides along theslot 28, one nib 53 of the conductive button 52 rides along anaffiliated collector strip 68.

The printed circuit 66 further includes a multitude of discreteelongated mutually parallel closely spaced electrically conductive tapsegments 80. The tap segments 80 arey disposed in parallel andpreferably rectilinear rows 82, each row of segments being parallel toand between two adjoining collector strips 68. The rows of tap segmentsare parallel to one another as well as to the slots 28. Within each row,the tap segments have their long axes parallel to the longitudinal axisof the casing 12, i.e. perpendicular to the length of the row. One sideof each row 82 of tap segments 80, i.e. the enlarged sides of all thesegments in each row, underlies a portion of an associated slot 28. Theother nib 55 of the button 52 rides along this side of an affiliatedrow.

The other (narrow) sides of the tap segments of each row 82 areelectrically connected by `a straight base ablatable resistance band 84,e.g. of carbon in a matrix of a synthetic resin, one such resistanceband being parallel to and electrically connecting the tap segments ofeach row 82. The resistance band 84 overlies the narrow segment ends,and the taps are thus electrically `connected to an aliated resistanceband at equidistantly axially spaced points. The material from which theresistance band 84 is formed may be silk screened over the metallicnarrow ends of the printed tap segments. A suitable product for thispurpose is Conductive Ink #EL-796, manufactured by the Advance ProcessCo. The Conductive Ink may be air dryed or force dryed, the lattermethod, under controlled temperature and humidity, reliably providing auniform resistance. Such ink essentially comprises a thermoplasticbinder dissolved in an organic solvent to form a liquid carrierthroughout which there is a heavy dispersion of line carbon powder.

Printed bus strips 86, 88 electrically interconnect llike ends of theresistance bands 84 in parallel, one bus strip 86 connecting the ends ofall the bands adjacent the front of the casing 12 to one input fixedcontact 70a and the other bus strip 88 connecting the ends of the bandsadjacent the rear of the casing 12 to another input fixed contact 70b.For convenience, the input contacts 70a, 701; are placed at oppositeends of the line of contacts.

FIG. 8 is a schematic electrical diagram of the printed circuit 66,showing yby way of example three potentiometer voltage pickos. Threeresistance components 90a, 90b and 90e are connected in parallel betweentwo input busses 92, 94 the latter being connected to a source ofelectrical potential. The busses 92, 94 of the schematic diagramrepresent, respectively, the busses 86, 88 of the printed circuit andthe resistance components 90 the resistance bands 84 and associated tapsegments 80 of the printed circuit. Movable contacts 96a, 9611 and 96Cpick off potential from their -ailiated resistance components,respectively 90a, 90b and 90e, at any points along the potential dropbetween the input busses 92, 94. The contacts in the schematic diagramare embodied `by the sliding bridge contacts 32. A lead 98 is providedto connect each of the schematic contacts 96 to a point external to thepotentiometer and is adapted to be electrically joined to an afliliatedcontrol circuit, the collector strips 68 and the fixed contacts 70 ofthe potentiometer 10 serving the same function as the leads 98.

The operation of my parallel ganged multiple poten tiometer 10 is, withthe previous description in mind quite simple. The endmost fixedcontacts 70a and 70b are electrically connected to the output terminalsof any suitable sour-ce of electrical potential. The busses 86 and 88will thereby be dierentially charged and a voltage drop will ensueacross each resistance band 84. Since each individual band has a uniformunit resistance lengthwise the voltage gradients along the dilferentbands will be the same even if the unit resistance of the differentbands are not alike.

Each sliding bridge contact 32 rides along a slot 28. When in anyselected position along the slot, the helical coil spring 58 urges theteeth 50 on the body 44 into engagement with the teeth 48 on theundersurface of the top wall of the shell and the button 52 intoelectrical contact with the printed circuit 66. When so engaged, thesliding bridge contact is locked against accidental and unintendedmovement as by unwanted vibration of the panel in which thepotentiometer 10 is installed. When it is desired to move the slidingbridge contact 32, the contact is pushed downwardly, overcoming the coilsprings biasing force, so that the head 40 rides on the raised lowridges 30 and so that the teeth 48, 50 are clear of one another. Thecontact is then pushed along the slot 28 in either di rection to anotherdesired position, whereupon it is released, the coil spring againengaging the teeth 48, 50 and locking the contact 32 in place.

As has been mentioned, the conductive button 52 has two conductive nibs.One nib 53 rides on and is in electrical contact with an associatedcollector strip 68, the latter being connected to a contact 70 and theother nib 55 rides on the enlarged sides of tap segments 80 in a row 82of such segments, each of the latter being connected at its narrow sideto successive points of the associated resistive band 84. The nib 55 isof suicient width and the tap segments are closely enough spaced so thatthe nib always contacts at least one but never more than two adjacenttap segments. The lines of the printed circuit on which the nibs 53, 5Sride 'are preferablyof hard electrically conductive material as rhodiumso that they do not wear out. The nibs 53, 55 through the bridge button52 interconnect any one or two tap segments 80 to an associatedcollector strip 68 at any point along the resistance band 84, therebypicking olf any desired potential drop between the busses 86, 88 andleading this voltage to the lixed contact 70. It will be noted that thenibs do not ride over the ablatable resistance bands 84 so that theresistance of the unit is not subject to variation due to abrasive wear.

The electrical device heretofore described houses and combines numerousindividually adjustable potentiometer voltage pickoffs in convenientclose proximity to one another and within a small and compact casing.The unit as a whole may be quickly mounted and easily manuallymanipulated by the hand of a user. The potentiometer 10 is particularlywell suited for mounting in a console or control panel.

The multiple ganged parallel potentiometer 10 with which a reader of theinstant disclosure is now familiar has particular value in use withstage and television lighting, and can be easily incorporated into alighting control circuit as disclosed in Izenour, United States LettersPatent Re. 23,575.

It thus will be seen that I have provided a device which achieves theseveral objects of my invention and which is well adapted to meet theconditions of practical use.

As various possible embodiments might be made of the above invention,and as various changes might be made in the embodiment set forth, it isto be understood that all matter herein described or shown in theaccompanying drawings is to be interpreted as illustrative and not in alimiting sense.

I claim:

1. For use with an electrical unit comprising a casing having a firstwall including a narrow elongated slot and a second wall, said secondwall being parallel to the iirst Wall, and circuit'means carried by thesecond wall of the casing, said circuit means including a lirstconductiveV strip parallel to the length of the slot' and a row of shortparallel conducting mutually spaced segments, each segment beingelongated, the length of each segment being transverse to the length ofthe row, the length of the row being parallel to the rst conductivestrip and to the slot, said row being adjacent to but spaced from therst conductive strip: a bridge contact mounted for sliding movementalong the slot, said bridge contact having a head disposed on the sideof the iirst'wall remote from the second wall, a body disposed on theother side of said rst wall so as to be between said walls, a neckpassing through the slot and joining the head to the body, the body ofthe contact being non-conductive and hollow, an electrically conductivebutton carried by the body, said button having portions projecting fromthe body toward the second wall, one portion being disposed incontinuous contact with the first elongated strip and the other portionbeing disposed to successively contact different segments of said row asthe bridge contact is moved along the slot, said bridge contact thusbridging and electrically connecting the lirst conductive strip to anypre-selected bridging Contact', being progressively movable along theslot in a direction parallel to the first conductive strip andtransversing to the breadths of the parallel segments, means mountingthe button for sliding movement in the body along a linear path towardand away from the circuit means, spring means carried by the body urgingthe button toward the circuit means, and means prohibiting rotation ofthe button within the contact whereby one button portion remains incontact with the first conductive strip in all positions of the bridgecontact and the other button portion remains in contact with diierentsegments in different positions of the bridging contact.

2. For use with an electrical unit including a first elongated memberhaving an electrical characteristic which varies continuously as afunction of position along said member, a bridge contact adapted toengage said member at various positions along its length, said Contacthaving a body which is electrically nonconductive and hollow, anelectrically conductive button carried by the body, said button having aportion projecting from the body toward the member and contacting saidmember, and spring means urging the button toward the member, the body0f the contact defining a cylindrical bore, the button being cylindricaland sliding axially within the bore linearly toward and away from themember, the body including a rst axial slot closed on its end closest tothe member, a second axial slot open on its endclosest to the. member,said' slots being spaced circumferentially of said bore, and atransverse slot connecting the other end of the rst slot and the secondslot, the button carrying a radially outwardly protruding tab of ashape` to be slidable in the slots, whereby the button is assembled withthe contact by sliding its tab into the second slot through its openend, then through the transverse slot and finally into the irst slot,the closed `end of the rst slot then limiting movement of the tab andthe button toward the member, andthe sides of the slot preventingrotation of the tab and the button in the contact, whereby said portionof the button remains in alignment with the member as the button movesalong the member in contact therewith.

3. The combination as set forth in claim 2 wherein the end of the boredistant from the member is closed, wherein the end of the bore distantfrom the member is closed, wherein the button is cup-shaped and opensaxially toward the closed end, and wherein the spring means comprises acoil spring situated within the bore between the closed end of thebutton and the closed end of the bore.

4l. The combination as set orth in claim 3 wherein the end of the springnearest the member is received within the button.

References Cited UNITED STATES PATENTS 2,688,679 9/1954 Schleuning338-194 X 3,307,133 2/1967 Wolff 3318-188 X 2,840,650 6/1958 Long 200-162,903,633 9/1959 Cother 338-188 X 3,146,320 8/1964 Long et al. ZOO-16 XRICHARD M. WOOD. Primary Examiner.

I. G. SMITH, Assistant Examiner.

1. FOR USE WITH AN ELECTRICAL UNIT COMPRISING A CASING HAVING A FIRSTWALL INCLUDING A NARROW ELONGATED SLOT AND A SECOND WALL, SAID SECONDWALL BEING PARALLEL TO THE FIRST WALL, AND CIRCUIT MEANS CARRIED BY THESECOND WALL OF THE CASING, SAID CIRCUIT MEANS INCLUDING A FIRSTCONDUCTIVE STRIP PARALLEL TO THE LENGTH OF THE SLOT AND A ROW OF SHORTPARALLEL CONDUCTING MUTUALLY SPACED SEGMENTS, EACH SEGMENT BEINGELONGATED, THE LENGTH OF EACH SEGMENT BEING TRANSVERSE TO THE LENGTH OFTHE ROW, THE LENGTH OF THE ROW BEING PARALLEL TO THE FIRST CONDUCTIVESTRIP AND TO THE SLOT, SAID ROW BEING ADJACENT TO BUT SPACED FROM THESECDUCTIVE STRIP: A BRIDGE CONTACT MOUNTED FOR SLIDING MOVEMENT ALONGTHE SLOT, SAID BRIDGE CONTACT HAVING A HEAD DISPOSED ON THE SIDE OF THEFIRST WALL REMOTE FROM THE SECOND WALL, A BODY DISPOSED ON THE OTHERSIDE OF SAID FIRST WALL SO AS TO BE BETWEEN SAID WALLS, A NECK PASSINGTHROUGH THE SLOT AND JOINING THE HEAD TO THE BODY, THE BODY OF THECONTACT BEING NON-CONDUCTIVE AND HOLLOW, AND ELECTRICALLY CONDUCTIVEBUTTON CARRIED BY THE BODY, SAID BUTTON HAVING PORTIONS PROJECTING FROMTHE BODY TOWARD THE SECOND WALL, ONE PORTION BEING DISPOSED INCONTINUOUS CONTACT WITH THE FIRST ELONGATED STRIP AND THE OTHER PORTIONBEING DISPOSED TO SUCCESSIVELY CONTACT DIFFERENT SEGMENTS OF SAID ROW ASTHE BRIDGE CONTACT IS MOVED ALONG THE SLOT, SAID BRIDGE CONTACT THUSBRIDGING AND ELECTRICALLY CONNECTING THE FIRST CONDUCTIVE STRIP TO ANYPRE-SELECTED BRIDGING CONTACT, BEING PROGRESSIVELY MOVABLE ALONG THESLOT IN A DIRECTION PARALLEL TO THE FIRST CONDUCTIVE STRIP ANDTRANSVERSING TO THE BREADTHS OF THE PARALLEL SEGMENTS, MEANS MOUNTINGTHE BUTTON FOR SLIDING MOVEMENT IN THE BODY ALONG A LINEAR PATH TOWARDAND AWAY FROM THE CIRCUIT MEANS, SPRING MEANS CARRIED BY THE BODY URGINGTHE BUTTON TOWARD THE CIRCUIT MEANS, AND MEANS PROHIBITING ROTATION OFTHE BUTTON WITHIN THE CONTACT WHEREBY ONE BUTTON PORTION REMAINS INCONTACT WITH THE FIRST CONDUCTIVE STRIP IN ALL POSITIONS OF THE BRIDGECONTACT AND THE OTHER BUTTON PORTION REMAINS IN CONTACT WITH DIFFERENTSEGMENTS IN DIFFERENT POSITIONS OF THE BRIDGING CONTACT.